Improve process exit status macros on MinGW

When a Windows program is terminated by a fatal exception, its exit
code is the value of that exception, as defined by the various
EXCEPTION_* symbols in the Windows API headers.  This commit emulates
WTERMSIG etc. by translating the fatal exception codes to more-or-less
equivalent Posix signals.

gdb/ChangeLog:
2020-01-06  Eli Zaretskii  <eliz@gnu.org>
	    Pedro Alves  <palves@redhat.com>

	* Makefile.in (COMMON_SFILES): Add gdbsupport/gdb_wait.c.
	* windows-tdep.c: New enumeration of WINDOWS_SIG* signals.
	(windows_gdb_signal_to_target): New function, uses the above
	enumeration to convert GDB internal signal codes to equivalent
	Windows codes.
	(windows_init_abi): Call set_gdbarch_gdb_signal_to_target.
	* windows-nat.c: Include "gdb_wait.h".
	(get_windows_debug_event): Extract the fatal exception from the
	exit status and convert to the equivalent Posix signal number.
	* cli/cli-cmds.c (exit_status_set_internal_vars): Account for the
	possibility that WTERMSIG returns GDB_SIGNAL_UNKNOWN.
	* gdbsupport/gdb_wait.c: New file, implements
	windows_status_to_termsig.
	* gdbsupport/gdb_wait.h (WIFEXITED, WIFSIGNALED, WEXITSTATUS)
	(WTERMSIG) [__MINGW32__]: Separate definitions for MinGW.

gdb/gdbserver/ChangeLog:
2020-01-06  Eli Zaretskii  <eliz@gnu.org>
	    Pedro Alves  <palves@redhat.com>

	* win32-low.c (get_child_debug_event): Extract the fatal exception
	from the exit status and convert to the equivalent Posix signal
	number.
	(win32_wait): Allow TARGET_WAITKIND_SIGNALLED status as well.
	* Makefile.in (OBS, SFILES): Add gdb_wait.[co].

1 files changed, 18 insertions, 2 deletions

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 2214caa..36a47f7 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -68,6 +68,7 @@
 #include "inf-child.h"
 #include "gdbsupport/gdb_tilde_expand.h"
 #include "gdbsupport/pathstuff.h"
+#include "gdbsupport/gdb_wait.h"
 
 #define AdjustTokenPrivileges		dyn_AdjustTokenPrivileges
 #define DebugActiveProcessStop		dyn_DebugActiveProcessStop
@@ -1627,8 +1628,23 @@ get_windows_debug_event (struct target_ops *ops,
 	  windows_delete_thread (ptid_t (current_event.dwProcessId, 0,
 					 current_event.dwThreadId),
 				 0, true /* main_thread_p */);
-	  ourstatus->kind = TARGET_WAITKIND_EXITED;
-	  ourstatus->value.integer = current_event.u.ExitProcess.dwExitCode;
+	  DWORD exit_status = current_event.u.ExitProcess.dwExitCode;
+	  /* If the exit status looks like a fatal exception, but we
+	     don't recognize the exception's code, make the original
+	     exit status value available, to avoid losing
+	     information.  */
+	  int exit_signal
+	    = WIFSIGNALED (exit_status) ? WTERMSIG (exit_status) : -1;
+	  if (exit_signal == -1)
+	    {
+	      ourstatus->kind = TARGET_WAITKIND_EXITED;
+	      ourstatus->value.integer = exit_status;
+	    }
+	  else
+	    {
+	      ourstatus->kind = TARGET_WAITKIND_SIGNALLED;
+	      ourstatus->value.sig = gdb_signal_from_host (exit_signal);
+	    }
 	  thread_id = current_event.dwThreadId;
 	}
       break;